Stoffel Vandoorne's miserable start to the season with McLaren-Honda has continued after the Belgian received a 15-place grid penalty for the Russian Grand Prix.
Vandoorne and Alonso had both received more MGU-H updates ahead of this race weekend with Honda hoping that it would lead to more reliable running.
However, with five minutes of FP1 remaining in Sochi, Vandoorne experienced yet more loss of power and Honda have sinced identified a fresh problem with the MGU-K component.
Due to the lack of time to fix the specific issue between the first and second practice session, McLaren-Honda have opted to give Vandoorne a brand-new power unit apart from the battery and control electronics.
The Belgian had already raced through four power unit changes already this season and a fifth here will see him slapped with a 15-place penalty for Sunday's race.
The new engine contains part of the updated spec that Honda ran at the two-day test in Bahrain, where Vandoorne was able to complete 81 laps.
A Honda statement said: "Suspected MGU-K issue with Stoffel's PU in FP1. The issue is under investigation.
"In the interest of time we opted to change PU. We hope to be back out on track during FP2.
"The MGU-H/TC will be Stoffel's fifth, which means he will receive 15 grid penalties for the race."
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